The operation of conventional silicon (Si)-based transistor devices is usually severely affected by the impact of radiation, in particular high-energy particles such as photons, heavy ions, neutrons, protons and electrons, resulting in occurrences of single-event upset, single-event latchup, single-event burnout, gamma-dot upset, total-dose exposure, etc. These effects significantly degrade the performance reliability of the devices and circuits operating in certain critical environments, e.g., in nuclear power plants, outer space missions, or other occasions where there exists prevalent exposure to ionizing radiations.
Devices built on silicon-on-insulator (SOI) wafers exhibit better radiation hardness than their bulk-Si counterparts given that a buried oxide (BOX) insulator layer prevents the charges generated in the substrate from being collected by the junctions of the SOI devices. However, electrons can still be produced within the active SOI film (even though the film is relatively thin, i.e., typically from about 80 nanometers (nm) to about 150 nm in radiation-hard applications) which makes the SOI devices subject to potential radiation damage. Moreover, in order to improve the reliability of electronic circuits operating under these harsh environments, additional redundancy in circuit design for error correction is usually required, which increases the cost and circuit complexity.
It would seem then that using a thinner active SOI film would produce better radiation-hard devices. However, in SOI devices, the carrier mobility degrades dramatically as the Si channel thickness decreases, thus compromising the device performance. See, for example, Tsutsui et al., “Mobility and Threshold-Voltage Comparison Between (110)- and (100)-Oriented Ultrathin-Body Silicon MOSFETs,” IEEE Trans. On Electron Devices, vol. 53, no. 10, pgs. 2582-2588 (2006). In addition, the present-day fabrication of SOI wafers involves either the high temperature (about 1,100 degrees Celsius (° C.)) bond-strengthening anneal as in Smart Cut wafers or the ion implantation as used in the production of SIMOX (Separation by Implanted Oxygen). Both methods lead to considerable amounts of defects, i.e., oxygen vacancies (on the order of 1012/cm2), in the BOX that can trap radiation-generated electrons and holes.
Therefore, radiation-hard transistor devices that do not experience the above-described drawbacks would be desirable.